The circulatory access for extracorporeal treatments such as hemodialysis, hemofiltration, plasmapheresis, cytopheresis, and component blood banking, poses special problems. Because of the quantitative nature of the extracorporeal processes, and due to the fact that clearance rates of selected substances from the blood are directly related to the rate at which blood flows to and from the system, high blood flow rates to the system are preferable. To achieve these high flow rates, e.g. in excess of 200 ml. per minute, large veins such as the subclavian or femoral veins are usually accessed by the catheters used to gain circulatory access for these treatments. These large veins are located deep, in close proximity to vital organs such as the heart, lungs, and viscera, and are difficult to puncture and lead to a higher incidence of complications due to the blind techniques that must be used.
In order to obtain high blood flow rates from portions of the circulatory system closer to the surface, various surgical techniques are employed, usually in the arm. The blood supply to the arm begins in the brachial artery which divides into three arteries, i.e., the interosseous, radial and ulnar arteries. Arterial blood flow is under relatively high pressure and has a relatively high velocity. After supplying the oxygen and nutritional needs of the tissues, the blood returns via a large number of veins in the arm, including the basalic and cephalic veins.
Since the blood brought to the arm by three arteries is returned through a multitude of venous channels, each venous channel carries a small fraction of the blood. This blood is under relatively low pressure and moves slowly, and the blood from the central veins cannot flow to the peripheral veins because of the one-way valves in the veins. Therefore, in their natural state the veins are not able to provide adequate blood flow for most extracorporeal treatments. Consequently, the surgical techniques referred to above are used to join one of the arteries in the arm with an adjacent vein, and diverting the arterial blood flow through the vein. Such a vein is known as a "fistula" and can be readily accessed to supply blood to the extracorporeal treatment system.
A fistula is typically accessed by either two single-lumen catheters or a single double-lumen catheter in order to provide simultaneous flow into and out of the vein. The use of single-lumen catheters requiring two needle punctures is yet to be replaced by the use of a single double-lumen catheter requiring a single needle puncture, largely because of a disproportionate increase in pain and trauma resulting from the larger puncture for the double-lumen catheter.
Double-lumen catheters and cannulas have employed both coaxial lumens and lumens adjacent to one another. It is now known, however, that the preferred lumen geometry includes two side-by-side semicircular lumens. Coaxial catheters and cannulas are described, for example, in McLaughlin U.S. Pat. No. 4,096,860; Sorenson et al. U.S. Pat. No. 4,099,528; Tursteegen et al. U.S. Pat. No. 4,202,332; and Udall Canadian Pat. No. 1,092,927. Dual-lumen catheters and cannulas having lumens adjacent to one another are described, for example, in Consalvo U.S. Pat. No. 4,098,275; Mahurkar U.S. Pat. No. 4,134,402; Belan Belguim Pat. No. 8,342,211; Jacobson et al. U.S. Pat. No. 4,180,068; Grimsrud U.S. Pat. No. 4,203,436; Uthmann U.S. Pat. No. 4,385,631; Mahurkar U.S. Pat. Des. 272,651; Edelman U.S. Pat. No. 4,403,983; and Martin U.S. Pat. No. 4,451,252.